Communication system



5 Sheets-Sheet l L. W. PARKER COMMUNICATION SYSTEM March 18, 1952 FiledSept. 11, 1946 March 18, 1952 L. w. PARKER COMMUNICATION SYSTEM4 FiledSept. 11, 1946 Afm.

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COMMUNICATION SYSTEM Filed sept. 11, 194e 5 Shams-sheet s I l 30,000 IS96. /200 INVENTOR.

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INVENTOR. UU/5 IM PAP/KEA ATTORNEY March 18, 1952 w. PARKERCOMMUNICATION SYSTEM 5 Sheets-Sheet 5 Filed Sept. 11, 1946 INVENTOR.OU/5* W. MRA/ff? Patented Mar. 18, 1952 COMMUNICATION SYSTEM Louis W.Parker, Jackson Heights, N. Y., assignor to Federal TelecommunicationLaboratories, Inc., New York, N. Y., a corporation of DelawareApplication September 11, 1946, Serial No. 696,119

This invention relates to a method and means for communicating voltagevariations over a single channel and'more particularly to theapplication of such method and means to a telautograph communicatingsystem.

In telautograph systems, the movement of a stylus or pencil across awriting surface is translated into horizontal and vertical voltagecomponents which are ordinarily transmitted as such. Similar to themethod used in transmitting television images, each such point asdetermined by its `vertical and horizontal coordinates has to be framedby suitable vertical and horizontal synchronizing pulsations. In theapplication of such telautograph systems for use by the police as twoway communication between police cars and a central station, greatdifficulties are apparent when ultra high frequencies are employed. Sucha .system thus applied is particularly difficult since, ultra highfrequencies are subject to extreme attenuation and much interferencewhen used among steel frame buildings which alsoY cause multiplereflections with consequent confusion at the receiving end. While lowfrequency may be used from the central station to all carssimultaneously, communication toward the center must be done on ultrahigh frequencies if a great number of cars are in operation. It isobvious, of course, that only the use of ultra high frequency affords asuicient number of separate communication channels.

It is an object of the present invention to provide a method and meansfor communicating the variation in at least two voltages simultaneouslyas applied to a telautograph communication system.

It is another object to provide a system of the type referred to whichestablishes communication by the transmission of information regardingthe variation of two voltages over a single narrow channel.

Still another object is to provide a system which employs an average lowpower with extremely high peak powers at times as required.

It is still a further object to provide a system which transmits thevariation of voltages by means of time modulated pulses having a Wrepetition rate.

Still a further object is to provide an improved synchronizing systemfor use with a communication systemes referred to above.

In accordance with my invention, I provide multiple telautograph systemwhich utilizes pulses suitably modulated for conveying informationregarding the variation of direct, cur- 6C1aims. (Cl.178-19) rentpotentials as they correspond to theverti-l cal and horizontaldisplacement of a Writing stylus. These direct current potentials aremade to generate corresponding pulses which are displaced in time asreferred to a synchronizing base depending on kthe amplitude of suchpotentials. The pulses conveying intelligence corresponding to thevertical and horizontal components of the stylus position are combinedinto a sing-le pulse which carries the intelligence insofar as itsposition in time is varied with respect to the synchronizing signal orframe. A single source serves to synchronize both the transmitter andreceiver with low radio frequencies carrying the synhcronizing pulses.The system thus transmits the intelligence pertaining to characterswritten by a stylus in the form of a single pulse for each synchronizingframe at'peak power and in the form oi a comparatively small number ofpulses over a period of time. At the receiver,the ultra high frequencypulses are made to reproduce the motions of the transmitting stylusthrough` the medium of a beam of a rotating cathode ray tube, preferablyof the long persistence vision type. In accordance with another featureof the invention, I provide a method for Synchronization or framingwhich avoids the displacement of the observed writing on the cathode raytube due to the improper selection from a given number of synchronizingframes or cycles. rl'his is done by enabling the selection of the propvercycle-to be controlled by means of the intelligence carrying pulses. if

A better understanding of my invention and the objects and featuresthereof may be had from a particular description of an embodimentthere--V the accompanying.v

Figs. 3, l and 5 are a Vseries of graphsindicatingcertain voltage andcurrent conditions of the system of Fig. l; I

Fig. 6 is a diagram of a central station receiv? ing circuit in blockand schematic form; and

Fig. 7 is an alternative form of the receiving circuit of Fig. 6incorporating my improved synchronizing selector for the receiver ofthe. system.-

Referring to the system shown in Figs-1j,.- a central station unitindicated' at Land blocked off in broken lines includes a mediumfrequency transmitter 2 including an antenna 3 which is adapted tocontinuously send out a radio frequency modulated by synchronizingfrequencies at 4800 and 60 cycles as well as voice signals of a stationoperator. The central station also comprises a visual messagereproducing unit 4 which includes a medium frequency receiver 5. The twosynchronizing frequencies as emitted 4by the transmitter 2 are picked upby a suitable antenna 6 of the receiver 5 for synchronizing theoperation of a reproducing cathode ray tube system at 1. It will, ofcourse, be understood that the two audio frequencies for synchronizingare given here for purposes of illustrations only and may have othersuitable values. A number of receiver-transmitter units as indicated at8, 9 and I which may be placed within individual police prowl cars areprovided with medium frequency receiver units as at II which receive thetwo synchronizing frequencies over an antenna I2 and also any voicesignals that may be emitted from the transmitter 2 which are reproducedby means of loud speaker I3. The synchronizing signals picked up byreceiver II are used to synchronize ultra high frequency transmitter I 4operatively associated with the respective receiver units. Thetransmitter includes a stylus or similar writing device I5 which servesto modulate the associated transmitters as at I4 in accordance with thevertical and horizontal displacements thereof. Signals, thus modulatedat ultra high frequencies are sent out over antennas I6 to be picked upby a U. H. F. receiver I1 over a suitable antenna I8 at the centralstation. These signals are subsequently made to act on the beam of thecathode ray type reproducing tube at 1 to become visible thereon in theform of legible characters.

In Fig. 2, one of the prowl car transmitter-re- 60 cycle output, afterfiltering, undergoes a full wave rectification in a rectifying circuit23. The A. C. component of the resulting pulsating unidirectionalcurrent is used for synchronizing a 60cycle blocking oscillator at 24.It is to be noted that an alternative method for obtaining asynchronizing signal is described in connection with Fig. 7. Theblocking oscillator 22 feeds into a sawtooth voltage generating circuitcomprised of an electron discharge vacuum tube 25 across which a storagecondenser 26 has been provided. The condenser 26 charges from a platesupply indicated at 21 over a resistor 23. The conductivity of theldischarge tube 25 is controlled by the blocking oscillator pulsations asapplied to grid 29 thereof. The condenser 26 has been selected so as toprovide a peak potential which is considerably lower than the platesupply voltage whereby a substantiall linear rise in voltage thereacrossis obtained. The sawtooth volt-k age thus obtained is applied to grid 30of a high- Cathode 32 of the tube 3I receives.

quency transformer 35 which acts to diiferentiate the plate current andto generate a voltage across a secondary thereof. Similar circuits andarrangements have .been provided for obtaining signcant votlages for thevertical component coordinate of the stylus 34; these include a sawtoothgenerating circuit 36, having a discharge tube 31, synchronouslycontrolled from the 60- cycle blocking oscillator 24, and a storagecondenser 38 which is charged from the plate potential source 21 over aresistance 39. The resulting 60 cycle sawtooth voltage is applied toanother high-mu triode shown at 40 which, in its plate circuit issimilarly provided with a high frequency transformer 4I. The triode 40receives modulating direct current voltages from a vertical componentcoordinate potentiometer 42, the output of which is applied to cathodecir cuit 43. The secondaries of the transformers 35 and 4I are tiedtogether over a connection 44 for supplying the combined vertical andhorizontal intelligence carrying voltages to a peak rider triode 45. Thepeak rider supplies inteligence conveying audio pulsations formodulating an ultra high frequency pulse transmitter 46 Which emitsoutbursts of radio frequencies, with peak intensities which involve 10to 50 kilowatts or more, the average power output, however, being about1/iooo of this peak value. Delaying for `the present, the description ofthe graphs of Figs. 3, 4 and 5, which will be discussed in connectionwith the operation of the apparatus, reference is now made to thereceiving apparatus as shown in Figs. 6 and 7 as they arel used at acentral station.

Receiving equipment for a ycentral station includes a medium frequencyreceiver 41, and 4800 and cycle filters 43 and r49 respectively, similarto those used in the prowl car receivers shown in Fig. 2. The receiveris also provided with 1200 and 60 cycle blocking oscillators 50 and 5Ias well as sawtooth generating circuits 52 and 53. The resulting highand low frequency sawtooth voltages for horizontal and vertical sweepingare changed into sawtooth currents by the method used in televisionreceivers, namely through the medium of vacuum tubes 54 and 55, andassociated transformers 56 and 51. The respective high and low frequencysawtooth current waves are applied to suitable deflection coils 58 and59 associated with a cathode ray tube 60 which is slowly rotated withrespect to the two coils by means of a motor 6I. The grid of thiscathode ray tube is fed from the output circuit of an ultra highfrequency receiver 62 which, by means of the antenna I3 mentioned inconnection with Fig. 1, picks up the U. H. F. signals from one of thetransmitting stations in the prowl cars. In the preferred type ofcathode ray tube as shown, the image appears on the side of the tube asat 63, while the latter is being rotated at a peripheral velocity ofabout 1 centimeter per second. The screen of this tube is of the longpersistence type retaining the image formed by consecutive dots for afew'seconds or if desired up to a minute.

These dots are about one millimeter in diameter and are located closeenough to one another to form substantially a continuous line.

In the receiving 'circuit shown in Fig.- 7, 'the general scheme issimilar to that described in Fig. 6. In this case, however, provisionhas been made to insure synchronization to the particular cycle of thehorizontal synchronizing frequency signal, that is, of the 4800 cyclefrequency, which is closest in time to the intelligence conveying nizethe blocking oscillator to any one of these.

cycles. It is obvious that synchronization to the wrong cycle woulddisplace the writing on the cathode ray tube. In the case illustrated inFig. 7, a cycle frequency has been employed for vertical synchronizingwhile the horizontal synchronizing is'achieved by the 4800 cycle frel'To select the proper cycle ofV quency as before. the synchronizingfrequency, pulses picked up by the U. H. F. receiver are utilized. Thecircuit diagram of the synchronizing-devices is shown boxed in by brokenlines at, 64. The output of the U. H.I F. receiver 62 is applied to atriode `65 and the filtered 4800 cycle signal is fed directly to anothertriode 66 in the synchronizing selector.

The two triodes 65 and 66 have their respective anodes 61 connected to aIcommon -potential source B+ and their respective cathodes `68 connectedtogether to ground respectively. The ground connection includes a commoncathode resistance 69. The synchronizing selector circuit is arrangedsuch as to receive both the signal pulses and the 4800 cycle Wave. Thetwo triodes 65 and 66 act as a cathode follower type electronic switchbetween the 4800 cycle nlter 48 and the 1200 `cycle blocking oscillator56. When pulses rst start to arrive from the receiver 62 they are 6sending out a succession of pulses which are noted in a panoramicreceiver at the central station. The receiver operator tunes the pulsereceiver to the proper frequency and gives the go-ahead signal over asuitable voice channel. The transmitting operator may then remove thestylus from its holder and commence the writing. Synchronization to the"proper cycle in accordance with the above is thusaccomplished a fewtenths of asecond after the pulse receiver is 4tuned in.

The operation Gf the transmitting .Circuit of Fig. 2 will be understoodby reference toFigs 3, 4, and 5.' In Fig. 3, there is shown in graplrtthe shape of the sav/tooth voltage iwave'as" afin plied to the grid 30of the high-mu triode 3l,"the

passed through the cathode follower 65 yto the blocking ,oscillator 50.These pulses are also applied to a diode 'l0 at avhigher potential, dueto the provision of alvoltageA dividing resistance r'Il across theoutput terminals at the receiver 62. This diode l0 causes theaccumulation of a charge across a comparatively high capacity'lignseries therewith. After a few pulses the voltage across this condenserbuilds up to a higher value than the peak potential applied to the gridof the tube 6'5. This has the effect of biasing the triode 65 beyond itsplate current cutoi.i That is to say,

condition the comparison triode 66 is almost biased to cut-olf by virtueof the high voltage across the resistance 69.

l4.5 the triode 65 normally has no lbias on its grid' when pulses arenot being received. Under this As the negative bias is increased on thetriode 65, the voltage across the cathode resistor 69 decreases puttingtriode 66 gradually into operation. Thus, in the beginning oftransmission, only the rst cathode follower, which receives the pulses,will operate, but after a few cycles the 4800 cycle signal takes overand the pulses are functionally eliminated. As long as pulses are dottedline at 13 showing the level ofthe DLC. voltage applied to thecathodeSZ. Over thepoi tion ofthe wave where the voltage issubstantially below the level of the cathode voltage there is no platecurrent. As the grid voltage rises, how ever, the point is'reached wherethe plate current starts to rise from zero.y With a high-Inulf'trifodethis rise is rapid until the grid current equals the current throughlthe resistance '28.. After this point. hasbeen reached the A.platecurrent remains constant until discharge tube 29 starts tocorlduct,-when the plate current againv rapidly drops' to zero. This is shown ingraph '.b on Fig. 3.

sult oflmotion of the stylus in the horizontal and'V vertical directionis a corresponding pulse .which is time modulated accordingly. In grapha of Fig. 4, a series of signicant horizontal coordinate pulses areshown, a vertical coordinate` pulse being illustrated in graph `b on thesame scale and showing that the eiective Width ofr 'aisingle verticalpulse is made to be substantially as much as the duration of one andone-quarter of a horizontal line sweep period. In graph c of Fig. 4, thesum of the horizontal and vertical pulses is shown graphically,` thedotted line at 'lli indicating the cut oif point of the peak rider t5.It will be apparent therefrom that only at being sent the triode remainscut off and only the triode 56 will operate supplying the 4800 cyclesignal to the 1200 cycle blocking oscillator. It

they would start the horizontal sweeping line in For the the receiver atthe proper instant.

proper operation of the synchronizing selector. ,j

provision must be made at the transmitting end to send at first a fewpulses at the beginning of the horizontal sweep, which may be simply .Y

done by leaving the stylus in the holder at the left side of the writingfield before use. To call the central station it is only necessary toturn on the pulse transmitter Without removing. the

stylus from its holder. This has the eifectof rare intervals do the twopulses of succeeding waves or cycles get past the peak rider. Usuallyonly one horizontal pulse effectively coincides and therefore getsthrough for each vertical pulse. In Fig. 5 an overall View of theinterrelation of the horizontal and vertical pulses has been provided.In this gure the heavy dots o-n the horizontal lines show where thehorizontal pulses occur and the heavy line shows the duration of thevertical pulses It is apparent that they coincide at only one pointwhere they form an observable pulse indicative of the combined verticaland horizontal pulses. Thus the locus of such points corresponds to thesuccessive resultant values of voltages varying with the compositehorizontal and vertical movement of the stylus.

While the above is a description of the prin- The plate current in graphb is sub-5. jected to differentiation-inthe transformer 35;'.

I claim:

1. A method for producingrnasingle channel signal for the variation oftwo'r independent unidirectional voltages comprising generating pulsesmodulated in position in respect to a time base associated therewith inaccordance with the amplitude variation with time of each of the twoindependent voltages, combining the resulting pulses, and obtaining agiven peak portion of those pulses which coincide as a signal indicativeof the variation of said two voltages. l

2. A system for obtainingfa significant single channel signal indicatingthe amplitude variation of two independent unidirectional voltages foruse with means for providing two voltages having significant amplitudevariations with time, comprising means for generating pulses eachmodulated in respect to a time base associated therewith in accordancewith the amplitude variation of each of said 4two independent voltages,means for combining said two time modulated pulses, and means forobtaining the peak amplitude portion of coinciding pulses 3. Atelautograph transmitting system, coinprising character tracing meansfor producing significant voltages respectively for independenthorizontal and vertical movements thereof, means for producinghorizontal and vertical time Ibases of given frequencies for saidmovements forming individual cyclic frames, means for producing a singlepulse which is significant of both the horizontal and the verticalposition of said tracing means, a pulse transmitter, and means formodulating the output of said transmitter by means of said single pulse.A

4. A transmitting system according to claim 3, wherein said charactertracing means includes a stylus and a potentiometer circuit controlledby the horizontal and vertical molvements thereof.

5. A system according to claim 3, wherein said time base means includesa synchronizing wave source for the horizontal and the verticalcoordinate 6. A system according to claim 3, wherein said single pulseproducing means includes means for derivingja .pulse for each of saidframes which is significant of the respective horizontal of said tracingmeans, means for deriving a pulse for each of said frames which issignicant of the vertical position of said tracing means, means forcombining the said significant horizontal and verticalxpulses, and meansfor obtaining the peak amplitude portion of coinciding pulses to producesaid single pulse.

LOUIS W. PARKER.

REFERENCES CITED The-following references are of record in the le ofthis patent:

UNITED STATES PATENTS NumberI Name Date 1,279,178 Tiffany Sept 17, 19182,168,047 Skellett Aug. 1, 1939 2,168,048 Skellett Aug. 1, 19392,168,049 Skellett Aug l, 1939 2,227,596 Luck Jan. 7, 1941 2,231,971Tubbs Feb. 18, 1941 2,280,707 Kell Apr 21, 1942 2,338,949 KupfmullerJan. 11, 1944 2,406,880 Young, Jr. Sept 3, 1946 2,411,062 Schade Nov.12, 1946 2,417,286 Bartels Mar. 11, 1947 2,418,116 Grieg Apr l, 19472,462,117 Mikkelson Feb. 22, 1949 2,490,891 Walton Dec. 13, 1949 FOREIGNPATENTS Number Country Date v 560,928 Great Britain Apr 27, 1944

